Field of the Invention
Embodiments of the present disclosure are directed in general to green-emitting, garnet based phosphors that are applicable to a number of different technologic areas, particularly backlighting applications. Specifically, the present disclosure is directed to lutetium-based garnets
Description of the Related Art
Embodiments of the present invention are directed to cerium-doped, garnet-based phosphors. YAG:Ce is an example of such a phosphor, and this compound has for some time been used in commercial markets generating white light from so-called “white light LEDs.” This latter term is a misnomer, since light emitting diodes emit light of a specific monochromatic color and not a combination of wavelengths perceived as white by the human eye, but the term is nonetheless entrenched in the lexicon of the lighting industry.
In comparison to other phosphor hosts, particularly those based on the silicates, sulphates, nitridosilicates, and oxo-nitridosilicates, YAG:Ce has a relatively high absorption efficiency when excited by blue light, is stable in high temperature and humidity environments, and has a high quantum efficiency (QE>95%), all the while displaying a broad emission spectrum.
If there is a disadvantage in using a YAG:Ce phosphor, and there is in certain applications, it is that the peak emission of this phosphor is too long (that is to say, too deep into the red), for use as a luminescent source in, for example, a backlighting application.
An alternative to YAG:Ce is the cerium doped Lu3Al5O12 compound (LAG:Ce), which has the same crystalline structure as YAG:Ce, a similar temperature and humidity stability as the yttrium-based compound, and likewise for quantum efficiency. Despite these similarities, LAG:Ce exhibits a different peak emission wavelength than its YAG counterpart; in the lutetium case, this peak wavelength is at about 540 nm. This emission wavelength is still not short enough, however, to be useful in backlighting applications.
Thus, what is needed in the art, particularly in the fields related to backlighting technologies, is a phosphor with a garnet structure and a peak emission wavelength shorter than that of either YAG:Ce or LAG:Ce.